The present study is designed to examine the expression of VDR, CaSR, PTH, Cyclin D1, Ki67 and PCNA and to find out its relationship with clinical parameters in parathyroid adenomas. Examination of the contribution of genes expression can elucidate the critical link between proliferation and functional abnormalities in parathyroid adenomas. Alternative to DNA and RNA, protein expression can provide a better understanding of this disease.